System, method, and computer-readable medium for user equipment handoff within an ip-femtocell network

ABSTRACT

A system, method, and computer readable medium for provisioning communication services by an IP-based femtocell network is provided. Service of a user equipment may be transferred from one femtocell to another femtocell via a femtocell handoff procedure. Femtocell systems of the femtocell network perform link quality measurements and may distribute the link quality measurements to neighbor femtocells. A femtocell system may periodically evaluate the link quality with the user equipment. If an evaluation is made that the user equipment needs to be transferred to another site, the servicing femtocell site may evaluate the most recent link quality measurements received from neighboring femtocell sites and select a femtocell site for handoff. In the event that the femtocell network is deployed in an area serviced by a macrocellular network, handoff routines may provide preference for transferring the user equipment to a target femtocell system rather than a macrocell site.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No. 12/252,202 entitled SYSTEM, METHOD, AND COMPUTER-READABLE MEDIUM FOR USER EQUIPMENT HANDOFF WITHIN AN IP-FEMTOCELL NETWORK filed on Oct. 15, 2008, which claims priority to U.S. provisional patent application Ser. No. 61/003,151 entitled SIP-IOS ADAPTER FUNCTION filed Nov. 15, 2007, the disclosure of each of which is incorporated in its entirety herein by reference.

FIELD OF THE INVENTION

The present invention is generally related to radio access technologies and, more particularly, to mechanisms for Internet protocol (IP) provisioning of a femtocell radio access network.

BACKGROUND OF THE INVENTION

Contemporary cellular radio systems, or mobile telecommunication systems, provide an over-the-air interface to wireless user equipments (UEs) via a radio access network (RAN) that interfaces with at least one core network. The RAN may be implemented as, for example, a CDMA2000 RAN, a Universal Mobile Telecommunications System (UMTS) RAN, a Global System for Mobile communications (GSM) RAN, or another suitable radio access network implementation. A UE may comprise, for example, a mobile terminal such as a mobile telephone, a laptop computer featuring mobile telephony software and hardware, a personal digital assistant (PDA), or other suitable equipment adapted to transfer and receive voice or data communications with the radio access network.

A RAN covers a geographical area comprised of any number of cells each comprising a relatively small geographic area of radio coverage. Each cell is provisioned by a cell site that includes a radio tower, e.g., a base transceiver station (BTS), and associated equipment. BTSs communicate with UEs over an air interface within radio range of the BTSs.

Numerous BTSs in the RAN may be communicatively coupled to a base station controller, also commonly referred to as a radio network controller (RNC). The BSC manages and monitors various system activities of the BTSs serviced thereby. BSCs are coupled with at least one core network.

BTSs are typically deployed by a carrier network in areas having a high population density. The traffic capacity of a cell site is limited by the site's capacity and affects the spacing of cell sites. In suburban areas, sites are often up to two miles apart, while cell sites deployed in dense urban areas may be as close as one-quarter of a mile apart. Because the traffic capacity of a cell site is finitely limited, as is the available frequency spectrum, mobile operators have a vested interest in technologies that allow for increased subscriber capacity.

A microcell site comprises a cell in a mobile phone network that covers a limited geographic area, such as a shopping center, hotel, airport, or other infrastructure that may have a high density mobile phone usage. A microcell typically uses power control to limit the radius of the microcell coverage. Typically a microcell is less than a mile wide.

Although microcells are effective for adding network capacity in areas with high mobile telephone usage, microcells extensively rely on the RAN, e.g., a controlling BSC and other carrier functions. Because contemporary BSCs have limited processing and interface capacity, the number of BTSs—whether microcell BTSs or typical carrier BTSs—able to be supported by the BSC or other RAN functions is disadvantageously limited.

Contemporary interest exists in providing enterprise and office access, including small office/home office (SOHO) radio access, by an even smaller scale BTS. The radio coverage area of such a system is typically referred to as a femtocell. In a system featuring a femtocell, a UE may be authorized to operate in the femtocell when proximate the femtocell system, e.g., while the UE is located in the SOHO. When the UE moves beyond the coverage area of the femtocell, the UE may then be serviced by the carrier network. The advantages of deployment of femtocells are numerous. For instance, mobile users frequently spend large amounts of time located at, for example, home, and many such users rely extensively on cellular network service for telecommunication services during these times. For example, a recent survey indicated that nearly thirteen percent of U.S. cell phone customers do not have a landline telephone and rely solely on cell phones for receiving telephone service. From a carrier perspective, it would be advantageous to have telephone services provisioned over a femtocell system, e.g., deployed in the user's home, to thereby reduce the load, and effectively increase the capacity, on the carrier RAN infrastructure. However, due the large potential demand for femtocell systems, contemporary BTS interface mechanisms with a RAN via BSCs or equivalent RNCs is impractical due to scaling issues.

Therefore, what is needed is a mechanism that overcomes the described problems and limitations.

SUMMARY OF THE INVENTION

The present invention provides a system, method, and computer readable medium for provisioning communication services by an IP-based femtocell network. An authorized user equipment may be serviced by the femtocell network, and service may be transferred from one femtocell to another femtocell via a femtocell handoff procedure. Femtocell systems of the femtocell network perform link quality measurements and may distribute the link quality measurements to neighbor femtocells. A femtocell system with which a user equipment is registered may periodically evaluate the link quality with the user equipment. If an evaluation is made that the user equipment needs to be transferred to another site, the servicing femtocell site may evaluate the most recent link quality measurements received from neighboring femtocell sites and select a femtocell site for handoff. In the event that the femtocell network is deployed in an area serviced by a macrocellular network, handoff routines may provide preference for transferring the user equipment to a target femtocell system rather than a macrocell site. In the event that a suitable femtocell is unavailable for handoff of the user equipment, the user equipment may be transferred to the macrocell site.

In one embodiment of the disclosure, a method for providing communication services to a user equipment is provided. The method comprises communicatively coupling a plurality of femtocell systems with a packet-switched backhaul, registering the user equipment with a first femtocell system of the plurality of femtocell systems, measuring a first radio interface quality between the user equipment and the first femtocell system, measuring a second radio interface quality between the user equipment and a second femtocell system, transmitting an indication of the second radio interface quality from the second femtocell system to the first femtocell system, and invoking a handoff procedure from the first femtocell system to the second femtocell system.

In another embodiment of the disclosure, a computer-readable medium having computer-executable instructions for execution by a processing system, the computer-executable instructions for providing communication services to a user equipment is provided. The computer-readable medium comprises instructions for communicatively coupling a plurality of femtocell systems with a packet-switched backhaul, registering the user equipment with a first femtocell system of the plurality of femtocell systems, measuring a first radio interface quality between the user equipment and the first femtocell system, measuring a second radio interface quality between the user equipment and a second femtocell system, transmitting an indication of the second radio interface quality from the second femtocell system to the first femtocell system, and invoking a handoff procedure from the first femtocell system to the second femtocell system.

In a further embodiment of the disclosure, a system for providing communication services to a user equipment is provided. The system comprises a packet-switched network having a domain with which the user equipment has a session initiation protocol service subscription, an Internet Protocol multimedia subsystem communicatively interfaced with the packet-switched network, and a femtocell network including a plurality of femtocell systems communicatively coupled with the packet-switched network. Each of the femtocell systems is adapted to provide a radio interface with the user equipment. The femtocell network includes a first femtocell system with which the user equipment is registered and that measures a first radio interface quality between the user equipment and the first femtocell system. A second femtocell system of the femtocell network measures a second radio interface quality between the user equipment and the second femtocell system and transmits an indication of the second radio interface quality to the first femtocell system. A handoff procedure is invoked to transfer service from the first femtocell system to the second femtocell system. The second femtocell system allocates a session initiation protocol user agent for the user equipment and submits a registration to a location service on behalf of the user equipment.

BRIEF DESCRIPTION OF THE DRAWINGS

Aspects of the present disclosure are best understood from the following detailed description when read with the accompanying figures, in which:

FIG. 1 is a diagrammatic representation of a network system that includes a cellular network adapted to provide macro-cellular coverage;

FIG. 2 is a diagrammatic representation of a conventional network system configuration featuring a femtocell;

FIG. 3 is a diagrammatic representation of a network system in which a femtocell system implemented in accordance with an embodiment of the present invention may be deployed;

FIG. 4A is a simplified diagrammatic representation of femtocell system depicted in FIG. 3 that may be connected with an IP backhaul in accordance with an embodiment;

FIG. 4B is a simplified diagrammatic representation of an alternative embodiment of a femtocell system that may be connected with an IP backhaul;

FIG. 5 is a diagrammatic representation of an exemplary session initiation protocol registration message generated by a femtocell system on behalf of a user equipment in accordance with an embodiment;

FIG. 6 is a diagrammatic representation of a network system featuring a femtocell network implemented in accordance with an embodiment;

FIG. 7 is a flowchart depicting a handoff routine for transfer of a user equipment from one femtocell system to another femtocell system in accordance with an embodiment;

FIG. 8 is a flowchart depicting a handoff routine that facilitates transfer of a user equipment from one femtocell system to another femtocell system in accordance with an embodiment; and

FIG. 9 is a diagrammatic representation of a registration message that may be submitted to a location service by a target femtocell system to which a user equipment is transferred during a handoff procedure in accordance with an embodiment.

DETAILED DESCRIPTION OF THE INVENTION

It is to be understood that the following disclosure provides many different embodiments or examples for implementing different features of various embodiments. Specific examples of components and arrangements are described below to simplify the present disclosure. These are, of course, merely examples and are not intended to be limiting.

FIG. 1 is a diagrammatic representation of a network system 100 that includes a cellular network 110 adapted to provide macro-cellular coverage to a user equipment. Cellular network 110 may comprise, for example, a code-division multiple access (CDMA) network, such as a CDMA-2000 network.

Cellular network 110 may include any number of base transceiver stations (BTSs) 112 a-112 c communicatively coupled with a base station controller (BSC) 114 or RNC. Each individual BTS 112 a-112 c under the control of a given BSC may define a radio cell operating on a set of radio channels thereby providing service to a user equipment (UE) 125, such as a mobile terminal. BSC 114 manages the allocation of radio channels, receives measurements from mobile terminals, controls handovers, as well as various other functions as is understood. BSC 114 is interconnected with a mobile services switching center (MSC) 116 that provides mobile terminal exchange services. BSC 114 may be additionally coupled with a packet data serving node (PDSN) 118 or other gateway service that provides a connection point between the CDMA radio access network and a packet network, such as Internet 160, and provides mobility management functions and packet routing services. MSC 116 may communicatively interface with a circuit switched network, such as the public switched telephone network (PSTN) 150, and may additionally be communicatively coupled with an interworking function (IWF) 122 that provides an interface between cellular network 110 and PSTN 150.

System 100 may also include a signaling system, such as a signaling system #7 (SS7) network 170. SS7 network 170 provides a set of telephony signaling protocols which are used to set up the vast majority of the world's PSTN telephone calls. SS7 network 170 is also used in cellular networks for circuit switched voice and packet-switched data applications. As is understood, SS7 network 170 includes various signaling nodes, such as any number of service control points (SCPs) 172, signal transfer points (STPs) 174, and service switching points (SSPs) 176.

BTSs 112 a-112 c deployed in cellular network 110 may service numerous network 110 subscribers. Cell cites provided by BTSs 112 a-112 c commonly feature site ranges of a quarter to a half mile, e.g., in densely populated urban areas, to one to two miles in suburban areas. In other remotely populated regions with suitable geography, site ranges may span tens of miles and may be effectively limited in size by the limited transmission distance of relatively low-powered UEs. As referred to herein, a cell provided by a BTS deployed in carrier network 110 for access by any authorized network 110 subscriber is referred to as a macrocell.

FIG. 2 is a diagrammatic representation of a conventional network system 200 configuration featuring a femtocell. In the depicted example, a central BSC 214 deployed in a cellular carrier network 210 may connect with a soft switch core 212 that is connected with a MSC 216. MSC 216 connects with the cellular core network and may interface with other networks, such as the PSTN as is understood. BSC 214 may be connected with and service numerous BTSs 212 a-212 c that provide macrocells to cellular network 210 subscribers.

BSC 214 may additionally connect with a tunnel gateway system 218 that is adapted to establish secured tunnels 232 a-232 x with respective femtocell systems 250 a-250 x. Femtocells comprise cellular access points that connect to a mobile operator's network using, for example, a residential DSL or cable broadband connection. Femtocells 250 a-250 x provide a radio access point for UE 225 when the UE is within range of a femtocell system with which the UE has authorized access. For example, femtocell system 250 a may be deployed in a residence of the user of UE 225. Accordingly, when the user is within the residence, mobile telecommunications may be provided to UE 225 via an air-interface provided by femtocell system 250 a. In this instance, UE 225 is effectively offloaded from the macro BTS, e.g., BTS 212 a, and communications to and from the UE are carried out with femtocell system 250 a over Internet 260. Thus, femtocell systems 250 a-250 x may reduce the radio resource demands by offloading UEs from macrocells to femtocells and thereby provide for increased subscriber capacity of cellular network 210.

In contemporary implementations such as that depicted in FIG. 2, a femtocell system 250 a comprises a transceiver without intelligence and is thus required to be connected and managed by BSC 214. Thus, femtocell systems 250 a-250 x are reliant on the carrier network centralized BSC 214 which has limited capacity and thus does not exhibit desirable scaling characteristics or capabilities. Moreover, high communications overhead are realized by the BTS backhaul.

FIG. 3 is a diagrammatic representation of a network system 300 in which a femtocell system implemented in accordance with an embodiment of the invention may be deployed. System 300 includes a radio access network (RAN) 310 that provides an over-the-air interface with a UE 325, e.g., a mobile terminal. RAN 310 may comprise, for example, a CDMA radio access network or another suitable RAN. RAN 310 may comprise various BTSs and associated base station controllers BSCs as well as other infrastructure as is understood. UE 325 may be implemented as a personal digital assistant (PDA), a mobile phone, a computer, or another device adapted to interface with RAN 310.

System 300 may include an IP Multimedia Subsystem (IMS) 320 architecture adapted to provide IP service to UE 325. To this end, RAN 310 is communicatively coupled with a serving general packet radio service (GPRS) support node (SGSN) 314 and a gateway GPRS support node (GGSN) 316. SGSN 314 provides the delivery of data packets from and to UE 325 within its service area. GGSN 316 provides an interface between the GPRS backbone network and external packet data networks. GGSN 316 is communicatively coupled with a policy decision function (PDF) 318 that provides authorization of media plane resources, e.g., quality of service (QoS) authorizations, policy control, bandwidth management, and the like. PDF 318 may be communicatively coupled with a call session control function (CSCF) 320.

CSCF 320 comprises various session initiation protocol (SIP) servers or proxies that process SIP signaling packets in IMS 320. CSCF 320 may include a proxy-CSCF (P-CSCF) that provides a first point of contact for an IMS-compliant UE. The P-CSCF may be located in the visited network, or in the UE's home network if the visited network is not fully IMS-compliant. UE 325 may discover the P-CSCF, e.g., by using Dynamic Host Configuration Protocol (DHCP), or by assignment in a packet data protocol (PDP) context. CSCF 320 additionally includes a Serving-CSCF (S-CSCF) that comprises the central node of the signaling plane. The S-CSCF comprises a SIP server, but additionally performs session control. The S-CSCF is located in the home network and interfaces with a home subscriber server (HSS) 340 to download and upload user profiles. CSCF 320 further includes an Interrogating-CSCF (I-CSCF) that comprises a SIP function located at the edge of an administrative domain. The I-CSCF has an IP address that is published in the Domain Name System (DNS) 372 that facilitates location of the I-CSCF by remote servers. Thus, the I-CSCF is used as a forwarding point for receipt of SIP packets within the domain.

HSS 340 comprises a user database that supports the IMS network entities that manage calls. HSS 340 stores user profiles that specify subscription-related information of authorized users, authenticates and authorizes users, and provides information about the user's physical location. Various application servers (AS) 342 a-342 n that host and execute services interface with CSCF 320 via SIP.

CSCF 320 is coupled with a breakout gateway control function (BGCF) 322 that comprises a SIP server that provides routing functionality based on telephone numbers. BGCF 322 is used when a UE places a call from the IMS to a phone in a circuit switched network, e.g., PSTN 330, or the public land mobile network. A media gateway controller Function (MGCF) 324 performs call control protocol conversion between SIP and ISDN User Part (ISUP) and interfaces with a signaling gateway (SGW) 326. SGW 326 interfaces with the signaling plane of a circuit switched network, e.g., PSTN 330. SGW 326 may transform lower layer protocols, such as Stream Control Transmission Protocol (SCTP), into the Message Transfer Part (MTP) protocol, and pass ISUP data from MGCF 324 to PSTN 330 or another circuit switched network. A media gateway (MGW) 328 interfaces with the media plane of PSTN 330 or another circuit switched network by converting data between real-time transport protocol (RTP) and pulse code modulation (PCM), and may also be employed for transcoding when the codecs of the IMS and circuit switched networks differ. Resources of MGW 328 are controlled by MGCF 324. Fixed access, e.g., IP telephony devices 374 a-374 b, may connect with IMS network via Internet 370 that is communicatively coupled with IMS network 320 by way of border gateway 360.

As is understood, DNS 372 comprises a scalable namespace that facilitates access to entities deployed on the Internet or private networks. DNS 372 maintains various records for host names, servers, and the like. For example, DNS 372 maintains records (commonly referred to as “A records”) that map hostnames to IP addresses, pointer (PTR) records that map IP addresses to canonical names to facilitate reverse DNS lookups, service (SRV) records that specify information on available services, naming authority pointer (NAPTR) records that facilitate regular expression based rewriting, and various other records. DNS 372 may additionally include a telephone number mapping (ENUM) system that facilitates resolution of SIP addresses from E.164 number as is understood.

A base station manager (BSM) 378 may be deployed in Internet 370 and may be adapted to communicate with numerous femtocell systems and femtocell networks. BSM 378 may provide various operations, maintenance, and management functions to femtocell systems. For example, BSM 378 may provide service provisioning of femtocell systems, e.g., by providing configuration downloads to femtocell systems and preloading default configuration data for femtocell systems distributed via sales channels. BSM 378 may provide various support and maintenance features, such as alarm and periodic statistics reporting, automatic remote software image distribution to femtocell system, provide upgrades and reconfigurations, and may provide remote access via Internet 370 for diagnostics and customer support.

In accordance with an embodiment, a femtocell system 350 may include integrated BTS and BSC (and/or radio node (RN) and radio network controller(RNC)) functions and may feature additional capabilities available in the provided femtocell site coverage area. Femtocell system 350 provides an IP-accessible radio access network, is adapted for operation with IMS 320, and provides radio link control functions. Femtocell system 350 may be communicatively coupled with Internet 370 via any variety of backhaul technologies, such as an 802.11x link, a 10/100 BaseT LAN link, a T1/E1 Span or fiber, cable set top box, DSL modem connected with a central office digital subscriber line access multiplexer, a very small aperture terminal (VSAT), or another suitable backhaul infrastructure.

In an embodiment, femtocell system 350 includes a session initiation protocol (SIP) adapter that supports a SIP client pool and provides conversion of call set-up functions to SIP client set-up functions. For example, a SIP client pool allocated by femtocell system 350 may comprise a plurality of SIP user agents 352 a-352 c that each may be allocated for a UE authorized to access femtocell system 350. Additionally, femtocell system 350 includes electronic serial number (ESN), and/or Mobile Equipment Identifier (MEID) screening, screening to allow only designated UEs to access the femtocell thereby restricting access to authorized home or small office UEs. For example, femtocell system 350 may be configured with an ESN and/or MEID list 354 that specifies ESNs or MEIDs of UEs authorized to access femtocell system 350. In the illustrative example, ESNs of “ESN 1”-“ESN 3” are included in ESN list 354. Provisioning of ESN(s) or MEIDs may be made as part of an initial femtocell system 350 activation. In the illustrative example, femtocell system 350 is allocated an Internet Protocol (IP) address of “66.249.73.42”, and UE 325 is allocated a mobile services ISDN (MSISDN) number, or E.164 number, of “12145551212”.

FIG. 4A is a simplified diagrammatic representation of femtocell system 350 depicted in FIG. 3 that facilitates provisioning of a femto-RAN in accordance with an embodiment. Femtocell system 350 includes an antenna 400 coupled with a BTS 410. BTS 410 may be implemented, for example, as a 1xRTT ASIC device and may comprise a non-diversity receiver featuring a built-in duplexer. In an embodiment, BTS 410 may feature only one operational band and may include a transmitter scan receiver and local oscillator. BTS 410 may be communicatively coupled with a BSC 420 that provides radio control functions, such as receiving measurements from UEs, such as mobile phones, control of handovers to and from other femtocell systems, and may additionally facilitate handoff to or from macrocells.

Femtocell system 350 includes an electronic serial number screening function 430 that may facilitate approving or rejecting service for a UE by femtocell system 350. Additionally femtocell system 350 includes an Internet Operating System (IOS) and SIP Adapter (collectively referred to as IOS-SIP Adapter 440). IOS-SIP adapter 440 may invoke and manage SIP clients, such as a user agent (UA) pool comprising one or more UAs. In accordance with an embodiment, each UE 325 authorized to be serviced by femtocell system 350 may have a UA allocated therefor by femtocell system in a manner that facilitates transmission of communications to and from a UE over an IP backhaul. Accordingly, when an authorized UE is within the femtocell system 350 site range, telecommunication services may be provided to the UE via the IP backhaul and femtocell system 350 provisioned RAN. When the UE is moved beyond the service range of femtocell system 350, telecommunication service may then be provided to the UE via macrocellular coverage.

To facilitate routing of calls from circuit switched call originators, femtocell system 350 may perform a DNS/ENUM registration on behalf of UEs authorized to obtain service from femtocell system 350. In the present example, assume UE 325 with a MSISDN of “12145551212” has a SIP service subscription in the domain “example.com” and has a SIP uniform resource identifier (URI) of “12145551212@example.com”. An example DNS/ENUM registration message generated by femtocell system 350 on behalf of UE 325 and transmitted to DNS 372 is as follows:

$ORIGIN 2.1.2.1.5.5.5.4.1.2.1.e164.arpa.

IN NAPTR 100 10 “u” “E2U+sip” “!̂.*$!sip:12145551212@example.com!”.

As is understood, the first line of the registration message comprises the MSISDN number of the UE converted (i.e., reversed with each numeral delineated with a “.” character and appended with the e164.arpa domain) for DNS lookup. The second line of the registration message specifies the NAPTR record for the hosts that can further process the address—the domain “example.com” (in which the UE with a URI of 12145551212@example.com is registered) in the present example.

In accordance with another embodiment, femtocell system 350 may generate and issue a SIP registration on behalf of UE 325 authorized for service access by femtocell system 350.

FIG. 4B is a simplified diagrammatic representation of an alternative femtocell system 450 that facilitates provisioning of a femto-RAN in accordance with an alternative embodiment. Femtocell system 450 includes an antenna 400 coupled with a radio node (RN) 411. RN 411 may be implemented, for example, as a 1xEV-DO ASIC device. For example, RN 411 may provide a 1xEV-DO Rev. 0 air interface or a 1xEV-DO Rev. A air interface. RN 411 may be communicatively coupled with a radio network controller (RNC) 421 that provides radio control functions, such as receiving measurements from UEs, control of handovers to and from other femtocell systems, and may additionally facilitate handoff to or from macrocells. RNC 421 may also provide encryption/decryption functions, power, load, and admission control, packet scheduling, and various other services.

Femtocell system 450 includes an electronic serial number screening function 430 that may facilitate approving or rejecting service for a UE by femtocell system 450. Additionally, femtocell system 450 includes an Internet Operating System (IOS) and SIP Adapter (collectively referred to as IOS-SIP Adapter 440). IOS-SIP adapter 440 may invoke and manage SIP clients, such as a user agent (UA) pool comprising one or more UAs. Each UE 325 authorized to be serviced by femtocell system 450 may have a UA allocated therefor by femtocell system 450 in a manner that facilitates transmission of communications to and from a UE over an IP backhaul. Accordingly, when an authorized UE is within the femtocell system 450 site range, telecommunication services may be provided to the UE via the IP backhaul and the femtocell system 450 provisioned RAN. When the UE is moved beyond the service range of femtocell system 450, telecommunication service may then be provided to the UE via macrocellular coverage. Femtocell system 450 may perform a DNS/ENUM registration on behalf of UEs authorized to obtain service from femtocell system 450 and may generate and issue a SIP registration on behalf of a UE authorized for service access by the femtocell system 450 in a manner similar to that described above with reference to femtocell system 350.

FIG. 5 is a diagrammatic representation of an exemplary SIP registration message 500 generated by femtocell system 350 on behalf of UE 325 authorized for service access thereby in accordance with an embodiment. Registration message 500 may be transmitted from femtocell system 350 to a location service, such as a SIP registrar implemented as SIP Registrar 380. Registrar 380 may provide the location and contact information to location service 382. Registration message 500 includes a REGISTER field 510 that specifies the registration is being made within the domain “example.com”. In accordance with an embodiment, multiple contacts are included in registration message 500. In the present example, registration message 500 includes a contact field 512 that specifies a SIP contact for UE 325. Notably, the SIP contact field 512 for UE 325 specifies the UA registered on behalf of UE with the URI 12145551212@example.com is located at the IP address of “66.249.73.42”. That is, the SIP contact registered by femtocell system 350 on behalf of UE 325 is to be addressed at the femtocell system 350 address of 66.249.73.42 thereby resulting in routing of SIP signaling messages to femtocell system 325. In turn, femtocell system 350 may convert SIP call set up messaging to RAN signaling, allocate an uplink and a downlink channel for UE 325, and set up a call or data session thereon.

In the present example, registration message 500 includes a second contact field 514 that specifies a telephone URI, e.g., the MSISDN +1-214-555-1212 of UE 325. Thus, a location query for the SIP URI sip:12145551212@example.com would return two contacts. The first is the SIP URI that can be used to reach femtocell system 350, and thus UE 325 thereby, and the second is the telephone URI that can be used to reach UE 325 via macrocellular coverage, i.e., via RAN 310. As is understood, the order of contacts 512-514 provides a contact preference, and the multiple contacts may be registered in separate registration messages. The depicted registration message including both the SIP contact URI and telephone URI is exemplary only. Accordingly, in the present example, an attempt to contact UE 325 may first be made via the SIP URI 12145551212@example.com. In the event that the session is not successfully set up via the SIP contact, an attempt may be made to setup a session via RAN 310 using the telephone URI.

When the UE 325 moves outside the coverage area of femtocell system 350, another registration may be generated and submitted by femtocell system 350 on behalf of UE 325 where the telephone URI is designated as the preferred contact. Further, the SIP URI may be removed from the registration when the UE 325 moves outside the coverage area of femtocell system 350 thereby avoiding any attempts to establish a session with UE 325 via femtocell system 350 when UE 325 has moved beyond the femtocell system 350 coverage area.

To better facilitate an understanding of disclosed embodiments, consider a call placed at circuit switched telephone 332 to UE 325. A gateway receives the call setup request, e.g., an Initial Address Message (IAM), and a query may be made with DNS 372 from which the domain “example.com” is resolved from the ENUM function. An INVITE message is then transmitted to the example.com domain which, in turn, resolves the location of the called UE 325. Particularly, CSCF 320 may interrogate location server 382 and determine UE 325 is registered as located at the IP address 66.249.73.42. Accordingly, the INVITE message is routed to proxy server 376 which forwards the INVITE message to femtocell system 350. Femtocell system 350 may then perform paging, channel allocation, and other procedures for provisioning a radio interface with UE 325 and issue SIP responses on behalf of UE 325. Thus, from a network perspective, femtocell system 350 appears as a user agent to which the call is directed. Further, UE 325 does not require a SIP client for receiving the call because femtocell system 350 advantageously performs signaling and media conversion for signaling and media transmissions over the air interface with 325. Thus, femtocell system 350 may appear as a conventional BTS to UE 325. A call from UE 325 to another terminal, such as circuit-switched telephone 332, a SIP client such as packet-switched telephony device 374 a, or another device, may similarly be facilitated by femtocell system 350.

As a second example, assume UE 325 has moved beyond the range of femtocell system 350. As noted above, femtocell system 350 may generate and transmit a registration message that excludes the SIP contact to facilitate provisioning of telecommunication services via macrocell coverage, e.g., via RAN 310. For instance, femtocell system 350 may periodically perform power measurements with UE 325, and upon the power measurement dropping below a particular power threshold, femtocell system may determine UE 325 is to be serviced by macrocellular coverage. Alternatively, a user may select macrocellular coverage via a user interface provided on UE 325. In this instance, UE 325 may provide an indication to femtocell system 350 that telecommunication services are to be provided by RAN 310. Other scenarios may similarly result in a determination that UE 325 is to be serviced by RAN 310. Upon such a determination, femtocell system 350 may generate and transmit a registration message on behalf of UE 325 to a registrar service, e.g., CSCF 320 and SIP registrar 380. The contact information may then be updated in location server 382 to indicate the telephone URI as the contact of UE 325. In this scenario, consider a call placed at circuit switched telephone 332 to UE 325. A gateway receives the call setup request, e.g., an Initial Address Message (IAM), and a query may be made with DNS server 372 from which the domain “example.com” is resolved from the ENUM service. An INVITE message is then transmitted to the example.com domain which resolves the location of called UE 325. In the present example, CSCF 320 may interrogate location server 382 and determine UE 325 has a preferred contact registered as a telephone URI of 2145551212. Accordingly, the INVITE message is routed to a gateway server, e.g., gateway server 390 which translates the INVITE message to a RAN-compliant call request signaling. The call may then be setup via RAN 310 accordingly.

In accordance with an embodiment, a network of femtocell systems may be deployed and connected with an IP backhaul. In this implementation, an authorized UE may be serviced by the femtocell network, and service may be transferred from one femtocell to another femtocell via a femtocell handoff procedure. In the event that the femtocell network is deployed in an area serviced by a macrocellular network, handoff routines may provide preference for transferring a UE to a target femtocell system rather than a macrocell site. In the event that a suitable femtocell is unavailable for handoff of a UE, the UE may be transferred to the macrocell site.

FIG. 6 is a diagrammatic representation of a network system 600 featuring a femtocell network implemented in accordance with an embodiment of the invention. System 600 includes a RAN 610 that provides an over-the-air interface with a UE 625, e.g., a mobile terminal. RAN 610 may comprise, for example, a CDMA radio access network or another suitable RAN. RAN 610 may comprise various BTSs 612 a-612 c and associated BSCs 604 as well as other infrastructure as is understood. Each of BTSs 612 a-612 c provide a respective macrocell 602 a-602 c that may provide telecommunication service to UE 625. BSC 604 is coupled with a MSC 606 that provides cellular exchange services, mobility management, and other services within the area that it serves as is understood.

RAN 610 may interface with IMS 620 adapted to provide IP service to UE 625. To this end, RAN 610 may be communicatively coupled with a SGSN 614 and a GGSN 616. GGSN 616 is communicatively coupled with a PDF 618 that provides authorization of media plane resources. PDF 618 may be communicatively coupled with a CSCF 620.

CSCF 620 comprises various SIP servers or proxies that process SIP signaling packets in IMS 620. CSCF 620 may include a P-CSCF, a S-CSCF, and an I-CSCF as is understood. HSS 640 stores user profiles that specify subscription-related information of authorized users, authenticates and authorizes users, and provides information about the user's physical location. Various application servers 642 a-642 n may host and execute services and is interfaced with CSCF 620 via SIP.

CSCF 620 is coupled with a BGCF 622 that comprises a SIP server that provides routing functionality based on telephone numbers. A MGCF 624 performs call control protocol conversion between SIP and ISDN User Part (ISUP) and interfaces with a SGW 626 that itself interfaces with the signaling plane of a circuit switched network, e.g., PSTN 630. A MGW 628 interfaces with the media plane of PSTN 630 or another circuit switched network. Resources of MGW 628 are controlled by MGCF 624. Fixed access devices, e.g., IP telephony devices 674 a-674 b, may connect with IMS network via Internet 670 that is communicatively coupled with IMS network 620 by way of border gateway 660.

Femtocell systems 650 a-650 c may include integrated BTS and BSC functions and may feature additional capabilities available in the provided femtocell site coverage areas. Femtocell systems 650 a-650 c provide an IP-accessible radio access network, are adapted for operation with IMS 620, and provide radio link control functions. Femtocell systems 650 a-650 c may be communicatively coupled with Internet 670 via any variety of backhaul technologies, such as an 802.11x link, a 10/100 BaseT LAN link, a T1/E1 Span or fiber, cable set top box, DSL modem connected with a central office digital subscriber line access multiplexer, a very small aperture terminal (VSAT), or another suitable backhaul infrastructure. In the illustrative example, femtocell systems 650 a-650 c are each coupled with an IP backhaul access device 655, such as an Ethernet cable or DSL router. For instance, femtocell systems 650 a-650 c may be coupled with access node 655 via respective 10/100BaseT twisted pair cables, Category 5 cabling, or other suitable interconnection.

Each of femtocell systems 650 a-650 c provide a respective femtocell site 651 a-651 c in which UE 625 may be provided telecommunication services over an air interface. Femtocell systems 650 a-650 c are communicatively coupled with one another via access device 655. Femtocells 650 a-650 c deployed for conjunctively providing a femtocell service coverage area comprised of the collective femtocell sites 651 a-651 c are collectively referred to herein as a femtocell network. In an embodiment, femtocell systems 650 a-650 c may exchange messages with one another to facilitate handoff of a UE from one femtocell to another, e.g., as UE 625 moves out of the radio range of a femtocell and into the radio range of another. In the depicted example, the femtocell network provided by femtocell systems 650 a-650 c is at least partially overlapped by one or more macrocell sites 602 a-602 c provisioned by macrocell BTSs 612 a-612 c. In such an implementation, femtocell systems 650 a-650 c may provide preference to another femtocell for handoff of a UE thereto. In the event that another femtocell is not available or is unsuitable for a handoff, the UE may then be transferred to macrocellular coverage via a handoff to a macrocell BTS.

In an embodiment, each of femtocell system 650 a-650 c include a respective SIP adapter that supports a SIP client pool and provides conversion of call set-up functions to SIP client set-up functions. Additionally, femtocell systems 650 a-650 c include ESN and/or MEID screening to allow only designated UEs to access the femtocells thereby restricting access to authorized home or small office UEs. Provisioning of ESN(s) or MEID(s) may be made as part of an initial femtocell system activation. In the illustrative example, femtocell systems 650 a-650 c are allocated a respective IP address of“66.249.73.42”, “66.249.73.43”, and “66.249.73.44”, and UE 625 is allocated a MSISDN number, or E.164 number, of “12145551212”.

Various power measurements may periodically be made by femtocell systems 650 a-650 c to monitor the communication link quality between a femtocell system and a UE. In the event that a link quality falls below a particular threshold, a handoff procedure may be invoked to transfer the UE to another femtocell system exhibiting a better radio interface quality with the UE, e.g., when the UE is moving away from one femtocell system and is reaching the periphery of the femtocell system's range while concurrently moving into another femtocell system's range. For example, femtocell systems 650 a-650 c may measure the pilot strength, e.g., the ratio of received pilot energy, Ec, to total received energy or the total power spectral density, Io, (the ratio commonly referred to as Ec/Io) in the pilot channel, such as the common pilot channel (CPICH). If the Ec/Io measurement falls below a predefined handoff threshold, the femtocell system may then attempt to identify a suitable femtocell system candidate for handoff of the UE. UEs may likewise perform power or link quality measurements, and in the event the power or link quality falls below a predefined threshold, the UE may issue a request to the source or servicing femtocell system for a handoff to another cell. For instance, a UE may periodically measure the Received Signal Code Power (RSCP), and request the source femtocell system perform a handoff if the measured RSCP falls below a predefined threshold.

In accordance with an embodiment, femtocell systems 650 a-650 c deployed in a network of femtocell systems may periodically transmit power measurements or other link quality metrics to other femtocell systems. Accordingly, if a source femtocell system determines a handoff should be performed, the source femtocell system may evaluate the most recent power measurements of other femtocell systems to identify a suitable candidate for handoff. In a similar manner, if a source femtocell system receives a request for handoff from a UE, the source femtocell system may evaluate the power measurement or other link quality metrics of other femtocell systems to identify a suitable candidate for handoff.

FIG. 7 is a flowchart 700 depicting a handoff routine that facilitates handoff of a UE from one femtocell system to another femtocell system in accordance with an embodiment. The processing steps of FIG. 7 may be implemented as computer-executable instructions processed by a source femtocell system currently servicing a UE and that may handoff a UE to another femtocell system. As referred to herein, a cell, e.g., provided by a femtocell system or a macrocellular system, to which a UE is transferred as the result of a handoff procedure is referred to as the target cell.

The handoff routine is invoked (step 702), and a link quality, such as Ec/Io, associated with a UE serviced by the femtocell system may be compared to a quality threshold (step 704). If the link quality is not less than the quality threshold thereby indicating a handoff is not required, the handoff routine cycle may then end (step 720). If the link quality is determined to be less than a quality threshold, the most recent link quality measurements received from other femtocell systems are read (step 706). An evaluation may then be made to determine if any of the link quality measurements of the candidate femtocell systems indicate a suitable candidate for handoff (step 708). If a suitable femtocell system candidate is not identified, a handoff to a macrocell site may then be made (step 710)—the implementation of which is outside the scope of the present disclosure. The handoff routine may then end according to step 720.

If a suitable femtocell candidate is identified for handoff at step 708, a handoff request may then be transmitted to the identified femtocell system (step 712). An evaluation may then be made to determine if the identified target femtocell system has accepted the handoff request (step 714). If the identified target femtocell system does not accept the handoff request, an evaluation may then be made to determine if another femtocell system is suitable for a handoff (step 716). If no additional femtocell system is suitable for a handoff, a handoff may then be made to a macrocell site (if available) according to step 710). If another femtocell system is identified as a suitable target femtocell system at step 716, a request for handoff may be transmitted to the identified femtocell system according to step 712.

Returning again to step 714, if the identified target femtocell system accepts the handoff request, handoff of the UE may then be completed with the target femtocell system (step 718), and the handoff routine cycle may then end according to step 720.

FIG. 8 is a flowchart 800 depicting a handoff routine that facilitates handoff of a UE from one femtocell system to another femtocell system in accordance with an embodiment. The processing steps of FIG. 8 may be implemented as computer-executable instructions processed by a target femtocell system to which a UE may be transferred as the result of a handoff procedure.

The handoff routine is invoked (step 802), and a handoff notification may be received from a source femtocell system currently servicing a UE for which a handoff is to be performed (step 804). The target femtocell system may then evaluate whether the femtocell system has available capacity to complete the handoff (step 806). If the target femtocell system does not have suitable capacity for transfer of the UE thereto, a handoff denial notification may be transmitted to the source femtocell system (step 808), and the handoff routine cycle may then end (step 820).

Returning again to step 806, if the target femtocell system has suitable capacity to complete the handoff, a handoff confirmation may be transmitted from the target femtocell system to the source femtocell system (step 810). The target femtocell system may then optionally allocate a forward and reverse channel for the UE to be transferred thereto (assuming the handoff is an active handoff) (step 812), and a user agent may be allocated by the target femtocell system for the UE (step 814). A registration for the UE may then be submitted on behalf of the UE (step 816). The registration may include the IP address of the target femtocell system as the preferred or current contact of the UE. The handoff process is then completed (step 818), and the routine cycle may then end according to step 820.

As an example, assume UE 625 is registered with femtocell system 650 a and has moved to the periphery of femtocell site 651 a. Femtocell system 650 a periodically measures a link quality with UE 625. Additionally, femtocell system 650 a may receive power measurements, such as Ec/Io measurements, from at least a subset, e.g., neighbor femtocells, of femtocell systems 650 b-650 c commonly deployed in the femtocell network with femtocell system 650 a. In an embodiment, each of femtocell systems 650 a-650 c may maintain a neighbors list that comprises a list of potential target femtocells for a handoff when it is necessary to transfer coverage of UE 625 to another femtocell. In this implementation, each femtocell configured as a neighbor of another femtocell may periodically transmit a power measurement to any femtocell having the particular femtocell listed as a neighbor. In the present example, assume femtocell system 650 b is the only femtocell listed as a neighbor and the only femtocell that transmits power measurements to femtocell system 650 a. Further assume that the power measured by femtocell system 650 a with UE 625 is determined to be less than a quality threshold that indicates a minimum link quality for maintaining service by femtocell system 650 a. In this instance, femtocell system 650 may evaluate the most recent power measured or other link quality metric of neighbor femtocell system 650 b to determine if femtocell system 650 b is a suitable handoff candidate according to step 708 of FIG. 7. Assume for illustrative purposes that the power measurement indicates femtocell system 650 b is a suitable candidate for handoff of UE 625. Accordingly, femtocell system 650 a may transit a handoff request to femtocell system 650 b according to step 712. Assume that femtocell system 650 b accepts the handoff request according to step 810. On receipt of the handoff confirmation, femtocell system 650 a may complete the handoff with femtocell system 650 b. To this end, femtocell system 650 b may allocate a forward and reverse link for UE 625 in the event that the handoff is an active handoff according to step 812, i.e., UE 625 is currently engaged in a call or data session. Additionally, femtocell system 650 b may allocate a SIP user agent for UE 625 and submit a registration message to a location service on behalf of UE 625 according to steps 814 and 816 of FIG. 8. For example, femtocell system 650 b may generate a SIP registration message similar to the exemplary registration message 900 depicted in FIG. 9. Notably, registration message 900 submitted by target femtocell system 650 b on behalf of UE 625 to be transferred thereto includes a contact field 910 that specifies the IP address (66.249.73.43 in the present example) of femtocell system 650 b as a contact for UE 625.

As described, a communication system featuring an IP-based femtocell network for provisioning communication services to a user equipment is provided. An authorized UE may be serviced by the femtocell network, and service may be transferred from one femtocell to another femtocell via a femtocell handoff procedure. Femtocell systems of the femtocell network perform link quality measurements and may distribute the link quality measurements to neighbor femtocells. A femtocell system with which a user equipment is registered may periodically evaluate the link quality with the user equipment. If an evaluation is made that the user equipment needs to be transferred to another site, the servicing femtocell site may evaluate the most recent link quality measurements received from neighboring femtocell sites and select a femtocell site for handoff. In the event that the femtocell network is deployed in an area serviced by a macrocellular network, handoff routines may provide preference for transferring the user equipment to a target femtocell system rather than a macrocell site. In the event that a suitable femtocell is unavailable for handoff of the user equipment, the user equipment may be transferred to the macrocell site.

The flowcharts of FIGS. 7-8 depict process serialization to facilitate an understanding of disclosed embodiments and are not necessarily indicative of the serialization of the operations being performed. In various embodiments, the processing steps described in FIGS. 7-8 may be performed in varying order, and one or more depicted steps may be performed in parallel with other steps. Additionally, execution of some processing steps of FIGS. 7-8 may be excluded without departing from embodiments disclosed herein.

The illustrative block diagrams depict process steps or blocks that may represent modules, segments, or portions of code that include one or more executable instructions for implementing specific logical functions or steps in the process. Although the particular examples illustrate specific process steps or procedures, many alternative implementations are possible and may be made by simple design choice. Some process steps may be executed in different order from the specific description herein based on, for example, considerations of function, purpose, conformance to standard, legacy structure, user interface design, and the like.

Aspects of the present invention may be implemented in software, hardware, firmware, or a combination thereof. The various elements of the system, either individually or in combination, may be implemented as a computer program product tangibly embodied in a machine-readable storage device for execution by a processing unit. Various steps of embodiments of the invention may be performed by a computer processor executing a program tangibly embodied on a computer-readable medium to perform functions by operating on input and generating output. The computer-readable medium may be, for example, a memory, a transportable medium such as a compact disk, a floppy disk, or a diskette, such that a computer program embodying the aspects of the present invention can be loaded onto a computer. The computer program is not limited to any particular embodiment, and may, for example, be implemented in an operating system, application program, foreground or background process, driver, network stack, or any combination thereof, executing on a single processor or multiple processors. Additionally, various steps of embodiments of the invention may provide one or more data structures generated, produced, received, or otherwise implemented on a computer-readable medium, such as a memory.

Although embodiments of the present invention have been illustrated in the accompanied drawings and described in the foregoing description, it will be understood that the invention is not limited to the embodiments disclosed, but is capable of numerous rearrangements, modifications, and substitutions without departing from the spirit of the invention as set forth and defined by the following claims. For example, the capabilities of the invention can be performed fully and/or partially by one or more of the blocks, modules, processors or memories. Also, these capabilities may be performed in the current manner or in a distributed manner and on, or via, any device able to provide and/or receive information. Further, although depicted in a particular manner, various modules or blocks may be repositioned without departing from the scope of the current invention. Still further, although depicted in a particular manner, a greater or lesser number of modules and connections can be utilized with the present invention in order to accomplish the present invention, to provide additional known features to the present invention, and/or to make the present invention more efficient. Also, the information sent between various modules can be sent between the modules via at least one of a data network, the Internet, an Internet Protocol network, a wireless source, and a wired source and via plurality of protocols. 

What is claimed is:
 1. A method, comprising: measuring a first radio interface quality between a user equipment and a first femtocell system; measuring a second radio interface quality between the user equipment and a second femtocell system; transmitting an indication of the second radio interface quality from the second femtocell system to the first femtocell system; and invoking a handoff procedure from the first femtocell system to the second femtocell system; wherein at least one of the first femtocell system and the second femtocell system periodically transmit one or more link quality metrics to one another.
 2. The method of claim 1, further comprising: determining, by the first femtocell system, that the first radio interface quality is below a predefined quality threshold; and determining, by the first femtocell system, that the second radio interface quality is sufficient for the handoff.
 3. The method of claim 1, further comprising: transmitting, by the first femtocell system, a request for handoff to the second femtocell system; and receiving, by the first femtocell system, a response accepting the handoff from the second femtocell system.
 4. The method of claim 1, further comprising allocating, by the second femtocell system, a user agent for the user equipment.
 5. The method of claim 4, further comprising transmitting, by the second femtocell system, a registration message to a location service on behalf of the user equipment, wherein the registration message includes an Internet Protocol address assigned to the second femtocell system as a contact for the user equipment.
 6. The method of claim 5, further comprising: receiving the registration message by the location service; and updating, by the location service, a location associated with the user equipment that specifies an Internet Protocol address assigned to the first femtocell system to the Internet Protocol address assigned to the second femtocell system.
 7. The method of claim 1, further comprising maintaining, by the first femtocell system, radio interface quality measurements for evaluation of a candidate femtocell system for handoff when the first radio interface quality is determined to be less than a quality threshold.
 8. The method of claim 1, wherein measuring the first radio interface quality is performed by the user equipment, the method further comprising transmitting, by the user equipment, a request for handoff to the first femtocell system.
 9. A non-transitory computer-readable medium having computer-executable instructions for execution by a processing system, the computer-executable instructions for: measuring a first radio interface quality between a user equipment and a first femtocell system; measuring a second radio interface quality between the user equipment and a second femtocell system; transmitting an indication of the second radio interface quality from the second femtocell system to the first femtocell system; and invoking a handoff procedure from the first femtocell system to the second femtocell system; wherein at least one of the first femtocell system and the second femtocell system periodically transmit one or more link quality metrics to one another.
 10. The non-transitory computer-readable medium of claim 9, further comprising instructions for: determining, by the first femtocell system, that the first radio interface quality is below a predefined quality threshold; and determining, by the first femtocell system, that the second radio interface quality is sufficient for the handoff.
 11. The non-transitory computer-readable medium of claim 9, further comprising instructions for: transmitting, by the first femtocell system, a request for handoff to the second femtocell system; and receiving, by the first femtocell system, a response accepting the handoff from the second femtocell system.
 12. The non-transitory computer-readable medium of claim 11, further comprising instructions for transmitting, by the second femtocell system, a registration message to a location service on behalf of the user equipment, wherein the registration message includes an Internet Protocol address assigned to the second femtocell system as a contact for the user equipment.
 13. The non-transitory computer-readable medium of claim 12, further comprising instructions for: receiving the registration message by the location service; and updating, by the location service, a location associated with the user equipment that specifies an Internet Protocol address assigned to the first femtocell system to the Internet Protocol address assigned to the second femtocell system.
 14. The non-transitory computer-readable medium of claim 9, further comparing instructions for maintaining, by the first femtocell system, radio interface quality measurements respectively obtained by at least a subset of the plurality of femtocell systems for evaluation of a candidate femtocell system for handoff when the first radio interface quality is determined to be less than a quality threshold.
 15. The non-transitory computer-readable medium of claim 9, wherein measuring the first radio interface quality is performed by the user equipment, the method further comprising transmitting, by the user equipment, a request for handoff to the first femtocell system.
 16. A system, comprising: a packet-switched network with which a user equipment has a session initiation protocol service subscription; an Internet Protocol multimedia subsystem communicatively interfaced with the packet-switched network; and a femtocell network including a first femtocell system and a second femtocell system, wherein the femtocell network: measures a second radio interface quality between the user equipment and a second femtocell system; transmits an indication of the second radio interface quality from the second femtocell system to the first femtocell system; and invokes a handoff procedure from the first femtocell system to the second femtocell system; wherein at least one of the first femtocell system and the second femtocell system periodically transmit one or more link quality metrics to one another.
 17. The system of claim 16, wherein the first femtocell system determines that the first radio interface quality is below a predefined quality threshold and determines that the second radio interface quality is sufficient for the handoff.
 18. The system of claim 16, wherein the first femtocell system transmits a request for handoff to the second femtocell system and receives a response accepting the handoff from the second femtocell system.
 19. The system of claim 16, wherein the second femtocell system submits a registration message to a location service on behalf of the user equipment, wherein the registration message includes an Internet Protocol address assigned to the second femtocell system as a contact for the user equipment.
 20. The system of claim 19, wherein the location service receives the registration message and updates a location associated with the user equipment that specifies an Internet Protocol address assigned with the first femtocell system to the Internet Protocol address assigned to the second femtocell system. 